High and low audiofrequency amplification control



R. w. HARVEY 1,761,626

HIGH AND LOW AUDIOFREQUENCY AMPLIFICATION CONTROL June 3, 1930.

Filed May 11, 1928 3 Sheets-Sheet 1 IC-RLQUEIYCY war/621231 R. w. HARVEY 1,761,626

HIGH AND LOW AUDIOFREQUENCY AMPLIFICATION CONTROL June 3, 1930.

Filed May 11, 1928 3 Sheets-Sheet 2 I Z N %%\J% m f JQW a 9% W W 1 6 9w Wu 6% MN U N5 N6 m5) NN a N. MKJQ 1 June 3,1930. I R. w. HARVEY HIGH AND LOW AUDIOFREQUENCY AMPLIFICATION CONTROL 5 Sheets-Sheet 3 Filed May 11, 1928 Patented June 3, 1930 UNITEDVSTA'TES not w. HARVEY, or CHICAGO, ILLINOIS HIGH AND LOW AUDIOFREQUENCY AMPLIFICATION CONTROL Application filed May 11,

This invention relates to an audio amplification system, and it pertains more particularly to a system adapted to be used selec tively with a phonograph or radio to vary tone quality and expression While a record is being played or a radio program is being received.

The object of this invention is to provide a system in which the value of notes of high frequency na; be varied, enhanced or suppressed withont appreciably affecting the value of the notes of low frequency, and in which the value of the notes of low frequency may be suppressed or' accentuated at will without appreciably affecting the value of the notes of high frequency, both of these regulations being separate and distinct from the ordinary volume control. The high register includes notes as produced by violin, flute,

q clarinet, soprano voice, etc., while the low register includes those produced by the tuba,

bass viol, kettle-drums, organ, etc.

- A further object of my invention is to provide an amplification system with audio fre- I quency controls to bring out the richness of the deepest bass or the delicate overtones of the highest soprano, or both, to suit the mood of the listener, or to correspond to the m tended expression of the composer or artist.

(The suppression of the upper register also eliminates needle scratch.)

A further object is to provide an amplifier cabinet with a volume control and with high and low register amplification controls in combination with a speaker located at a distance therefrom whereby the microphonic noises 'set up by the vibration of the speaker will not affect the tubes or cause electrical disturbances in the amplifier, and whereby a lis- 40 tener seated-by the amplifier controls may regulate the expression of the music while the speaker is located at an acoustlcally correct position in the room. p

A further object is to provide an improved 5 electrical circuit for independently varying the amplification ofthe high register and low register vibrations during the reception thereof. a 1 1 I A further object is to provide a compact arrangement of radio and phonograph pick-up,

1928. Serial No. 277,014.

an audio amplifier, audio controls, and a power supply therefor.

Other objects will be apparent as the de-' tailed description of my invention proceeds.

My invention may be briefly characterized as a system which makes use of capacity in series with a variable resistance which acts as a variable frequency-cutoff, said cut-off being shunted across the grid circuit of the first amplifier stage for controlling the high register,-a similar capacity and variable resistance being connected in series across the audio impedance coupler for controlling the low register, and a variable resistance being shunted across the grid circuit of the second amplifier circuit for volume control.

The outstanding feature of this arrangement is that the tone quality or'the relative values of the upper or lower register notes may be regulated while the record is playing. Variousfspeakers are designed to bring out certain frequencies'and the better speakers have been designed to respond throughout a very large range, but these speakers are not intended to be changed while music is being played. The present invention may be compared to the stops of an organ, which bring out the richness and fullness of certain frequencies, while suppressing other frequencies.

It should be noted that while the high and low register amplification controls are independent ofeach other and affect different portions of the amplification-frequency curve, the

shape of the curve as a whole is dependent on the position of both controls. In other words, it is the shape of the entire amplificationfrequency curve that determines thetone quality and amplification characteristics of the sound reproduction, and since each of the controls has a diiferent effect on the shape of this curve, each is dependent on the other and coacts therewith to produce a curve of the desired shape, as will be hereinafter pointed out.

In the accompanying drawings which represent a preferred embodiment of my invention, and in which similar parts are designated by like reference characters throughout the severalviews: s

Fig. 1 is a perspective of my improved phonograph amplifier cabinet and speaker unit, part of the amplifier cabinet being broken away to illustrate the tone control;

Fig. 2 is a plan view of the top of the cabinet shown in Fig. 1;

Fig. 3 is a graph illustrating the effect of the high register and low register controls as compared with the volume control;

Fig. 4 is a diagrammatic representation of the entire system, showing the relative arrangement of the pick-up amplifier contro1s,etc.;

Fig. 5 is a wiring diagram of a combination transformer-coupled impedance'-coupled, and push-pull-coupled amplifier circuit provided with my high register, low register and volume controls;

Fig. 6 is a modified volume control; and

Fig. 7 is a modified low register control.

In Fig. 1, I have shown the phonograph and/or radio cabinet 10 provided with a suitable cover 11 and a rotatable turntable 12 with which cooperates the swinging arm 13 carrying the pick-up device 14, the needle of which cooperates with grooves in a record 15 carried by the rotatable table 12. Ad acent the rotatable table I have provided a control panel 16 carrying a switch 17 for controlling the power supply to the amplifier and to the turntable motor, a control 18 for regulating the volume of the reproduced sound generally, a control 19 for suppressing or enhancing the high register notes, and a control 20 for similarly affecting the low register notes. I may also provide suitable receptacles 21 for records and other features which are characteristic of phonographs of this type. v

A jack 22 is provided at one end of the cabinetto receive the plug for connecting my amplifier system with a radio receiving set. This jack, of course, could be omitted and the receiving set built into the cabinet without departingfrom my invention.

In the bottom of the cabinet I provide an .opening 23 through which extends a cable- 24 carrying the necessary conductors for actuatin the speaker 40 which is mounted in a suita le cabinet 25. I prefer to use an electrodynamic speaker of the electromagnet movable coil type, although any suitable speaker may be used which will respond to the necessary frequencies. Whenit is desired to use a speaker of the fixed magnet type, however, provision must be made in the filter circuit to take the place of impedance 59, which, in my device, serves both as a coil for the electromagnet and as a choke in the filter circuit.

It will be apparent that the operator or listoner may sit adjacent the cabinet 10, select any desired records, and vary the tone qualit amplification, or relative value of notes of the u per and/or lower register at will, the s ea er being placed at some distance there om according to the acoustics of the room. The person playing the records can readily change needles and records without the necessity of getting up from the chair, and at the same time he can enjoy the music because the loud speaker is not at'his ear but at the end of a thirty-foot cable and placed in the most acoustically perfect position in the room. While this expedient has been'used with radio receivers, 1t is unique with phonographs, and in addition to the feature above stated, it eliminates the effect which the low note vibration of the speaker diaphragm would otherwise have upon the tubes and the electrical characteristics of the amplifier system.

Fig. 3 shows diagrammatically the effect of the three controls, the curves representing on an exaggerated scale the amplification-frequency characteristics of the speaker. The

.volume control 18 changes the amplification (ordinates) of the conventional curve A(l8) without changing the shape of the curve as is shown by the dotted line A. When the high register control 19 is turned to decrease the resistance 19R, the high frequency register is suppressed, and since the low register remains substantially unaltered, we have an entirely difierent amplification-frequency curve B(19). When the low frequency control 20 is turned to decrease resistance 20R, the low frequency register is accentuated to give an amplification-frequency curve in which the low register predominates C(20).

From an inspection of this graph (Fig. 3), it will be evident that elevating the low frequency portion of the curve is not, as would be expected, equivalent to lowering the high frequency part of the curve, because the resultant curve shape or speaker-amplifier characteristic is entirely different in these two cases. Controls 19 and 20 cooperate to determine the curve shape while control 18 changes the ordinates of this curve without affecting its shape.

Referring to Fig. 4, the pick-up 14 is'connected by suitable conductors 26 to a jack 27 adapted to receive a plug whereby flexible members 28 are disconnected therefrom when connected to a radio receiving set. In either case the signal from the pick-up or radio receiver is transmitted through conductors 29 to a plug 30 which also carries the conductors leading to the control dials. Thus the conductors 31 and 32 lead to the volume-control 18, conductors 33 and 34 to the high register control 19 and'conductors 35 and 36 to the low register control 20. (See Figs. 4 and 5.) All of these conductors lead to the single plug 30 which is provided with the necessary number of contacts, and which may be inserted in a suitable socket 30S in much the same manner that a radio tube is inserted in its'socket.

A second plug 37 carries the'wires 38v and 39, which are enclosed in cable 24 extending through the hole 23 in the bottom of the cabilamp 48, which in turn is connected by con-.

by conventional plug 41.

net l tljand which lead to the speaker cabinet 25. Wires 38 are connected to the electromagnet coil of the speaker and wires 39 to the movable coil thereof, as-will be apparentleads from this socket to a terminal of switch 17 A conductor 43 leads from the other terminal of switch 17 to a terminal of socket 44, the other terminal of which is connected by conductor 45 to plug 41. A conductor 46 leads from conductor 43 to a'pilot light 47 connected in series with record compartment ductor 49 to conductor 45. It will be obvious that the record compartment and pilot lights will be turned on when switch 17 is actuated and that they will indicate the fact that the system is connected to the power source.

A plug 50 cooperates with socket 44 andis connected by conductors 51 to a fuse block 52. The fuse block serves as a protection to limit both the current to the amplifier through conductors 53 and the current to the motor through conductors 54, socket 55and plug 56. The motor 57 may be of any suitable type and is controlled by switch 17 ",as is shown in Fig. 4.

The wiring diagram of the amplifier system is shown in Fig. 5, this circuit being mounted as a unit in the system and being re movable therefrom as above described.

The conductors 53 (see Fig. 4) are connected to the primary of transformer 58 (see Fig. 5) which supplies the necessary power for operating audio amplifier tubes I and II, push-pull amplifiers III and IV, and rectiative bias is provided by means of a suitable resistance 61. Impedances 59 and 62 cooperate with the various condensers to eliminate ripple, etc., as -is well known in the art.

The volume control is preferably a variable resistance 18R of about 200,000 ohms,

which is connected between the grid ofthe.

second audio amplifier tube II and the negative side ofthe circuit by conductors 32 and 31, respectively. This, in effect, by-passes the energy and is commonly known as a loss method. It may be applied across the grid A conductor 42 circuits in either the first or second stages or across the pick-up, and its position inthe second stage is shown in Fig. 5. An increase in the resistance 18R increases the energy supplied to the grid, and therefore increases the amplification ofv all frequencies, i. e., increases the volume (see Fig. 3).

Other methods may be used to vary the volume, such as, for instance, the potentiometer method illustrated in Fig. 6, wherein the v pick-up circuit is connected to a resistance 61 and a drop is taken from any portion of this resistance and fed into the input of the amphfier by means of conductor 62.

The high register control preferably comprises acondenser 33C of about .03 microfarads connected in series with a variable resistance 19B of 200,000 ohms, said ele ments being connected from the grid of thefirst amplifier to the negative side of the circu1t. In this arrangement a variation of the resistance varies theeffective capacity shunt, thereby varying the frequency cutoff in accordance with the formula:

1 21rfC X =impedance of the'coupling frequencyof the signal =capacity of the coupling Condenser 33C will by-pass high frequenc1es much more readily than low frequencies, and by rendering the condenser shunt more or less-effective by means of the variable reregisternotes.

The low register control comprises a condenser 35C of about .03 microfarads in series with a variable resistance 20B of 200,000 ohms. these elements being. connected in series across the audio impedance coupling 64. The choke coils 65 do not form an inductive' coupling but act as an impedance coupler between the plate circuit of the first amplifier and-the grid circuit of the second amplifier. The fixed resistance 63 prevents oscillation when the resistance 20R is cut out.

It will 'be evident that a variation in resistance 20R will vary the oscillation constant and will have a damping effect on the two impedance circuits into which it is connected, thus suppressing the low frequency signals transmitted from one stage to the next without materially affecting the high frequency signals. An increase in resistance 20R decreases the amplification or volume of low register notes.

In Fig. 7, I have shown a modification of creases the amplification or volume of high Ill this control where resistance 66B is connected in the rid circuit of the second stage.

It will t erefore be apparent that my three controls have separate and distinct functlons and that each cooperates with and is depend out upon the other for varying bot-h the shape and the ordinates of the amplification-frequency curve representing speaker-amplifier characteristics, as shown in Fig. 3.

While I have specifically described a preferred embodiment of my invention, it is understood that I am not limited to the details set forth therein except as defined by the following claims.

I claim:

1. In an audio frequency amplifier system, means for controlling the amplification of the volume throughout the entire frequency range, means for varying the amplification of low frequency without appreciably affecting the high frequencies and means for varying the amplification of high frequencies without appreciably affecting low frequencies.

2. In an amplifier system of the type wherein two stages are connected in cascade by impedance coupling, means for controlling amplification of the entire fre uency band, a variable resistance and a con enser connected in series across the impedance coupling for varying the low register, and a variable resistance and a condenser connected in series across a grid circuit for varying the high register.

3. In an amplifier system of the type wherein two stages are connected in cascade by impedance coupling, means for varying the high frequency signals without materially affecting low frequency signals, and means including a variable resistance connected between the plate of the first stage and the grid of the second stage whereby the low frequenc signals are limited without malterially a ecting the high frequency signa s.

4. In an audio amplifier system including two stages of amplification connected in cascade by impedance coupling, a variable resistance in series with a capacity connected from the grid of the first stage to ground and a variable resistance and a condenser connected in series across the impedance coupling.

5. In combination, a plurality of amplifier tubes, connections associated with said tubes to complete a single amplifier system, each tube being connected to amplify both high and low frequency si nals, said connections including means For varying the amplification of high frequency signals in said amplifier system without ap reciably affecting the amplification of'low requency signals, means for varying the amplification of low frequency signals without appreciably affecting the amplification of the high frequency signals, and independent controls feractuating said means, whereby the tone characteristics may be varied While the signal is being amplified.

6. In an amplifier system comprising a plurality of tubes connected to amplify both and whereby the position of the curve is varied without appreciably affecting its shape, and independent means for varying the high or low frequencies whereby the curve shape may be varied Without appreciably affecting the position of the curve.

7. In an amplifier system having a plurality of stages, means for varying the low frequency signals without materially affecting the high frequency signals, and means including a variable resistance connected in series with a condenser across the grid circuit of the first stage whereby the high frequency signals are limited without materially affect-- ing the low frequency signals.

8. In an amplifier system of the type where two stages are connected in cascade by impedance coupling, means for varying the high frequency signals Without materially affecting the low frequency signals, means including a variable resistance connected between the plate of the first stage and the grid of the second stage whereby the low frequencies are limited without materially affecting the high frequency signals, and independent controls for actuating each of said means, said controls being accessible for operation while sound is being amplified whereby tone qualities and characteristics may be continuously modified. I

9. In an amplifier adapted to'give a characteristic speaker-amplifier curve shape, means for varying the degree of amplification of the entire wave length band whereby the position of the curve is varied without appreciably affecting the curve shape, independent means for varying the high or low frequencies whereby the curve shape may be varied without appreciably affecting the position of the curve, and controls associated with each of said means whereby the tone qualities. and characteristics may be continuously changed while sound is being reproduced.

In witness whereof, I'hereunto subscribe my name this 9th day of May, 1928.

ROY W. HARVEY. 

